Issue: total base shear is not the sum of modal values

Issue

The total base shear value does not correspond to the sum of modal base shear values

Linear calculation protocol of a seismic load case

The user expects, that the total base shear forces is the sum of the values for each mode in the table, i.e.

which are not the values provided in the output table.

Explanation

The total base shear forces Fx and Fy at the bottom of the summary table of seismic load cases in the linear calculation protocol show the modal superposition value of the modal components, not the sum.

In the presented example, SRSS superposition is used. The correct calculation is

The same applies for the moments M_x and M_y.

For more information about modal superposition techniques, see the related theoretical background.